Realising Japan was losing the war, on 7 September 1944, in a session of the Japanese parliament, Prime Minister Kuniaki Koiso promised independence for the [Dutch] 'East Indies' at "sometime in the future".
[2] The Japanese navy was not supportive of the idea, but the 25th Army in Sumatra established a Central Advisory Council, headed by Mohammad Sjafei, which met only once.
Despite navy opposition, army-navy liaison vice-admiral Maeda Tadashi began to fund speaking tours by Indonesian nationalists Sukarno and Hatta.
The BPUPK was announced by the Sixteenth Army commander Lieutenant General Kumakichi Harada on 1 March 1945 to work on "preparations for independence in the region of the government of this island of Java".
[1][5][6] In the three months before the committee was established, a 19-member advisory board, or Sanyo Kaigi chaired by Sartono discussed the organization, agenda and membership of it.
It opened with a speech by the commander of the Japanese 16th Army, Lieutenant General Yuichiro Nagano, who said that independence was being granted to Indonesia to ensure good relations with Japan in the long term.
On 31 May, Professor Soepomo called for an authoritarian integralistic state based on a combination of the systems in Nazi Germany and Imperial Japan, with a strong executive.
[11] On the final day, 1 June, Sukarno made his famous speech in which he outlined the Pancasila - the five principles that would form the ideological basis of the new state.
[12] At the end of the BPUPK session, members were encouraged to discuss their views and hear opinions from the people at meetings held in their hometowns.
Of the 47 people invited, 38 met and, prompted by Sukarno, established a nine-member committee, the panitia sembilan, to work on a draft constitution.
The main opposition to Soepomo's integralistic concept came from Muhammad Yamin, who favoured a liberal democracy similar to the United States, with separation of powers and a bill of rights.